Argo Floats

Summary

Argo Australia provides real-time observations of the oceans around Australia by maintaining an array of autonomous profiling floats. Argo floats measure temperature and salinity from 2000 m depth to the surface every 10 days. Data is publically available from Global Data Access Centres within 24 hours of collection via the real-time data stream. Highly quality-controlled data is available after 12 months as part of the delayed mode data stream. Argo provides essential and in situ data for ocean and climate research and prediction/re-analyses.

The primary goal of the Argo program is to maintain a global array of autonomous profiling floats integrated with other elements of the climate observing system.

The specific aims are to:

detect climate variability over seasonal to decadal time-scales including changes in the large-scale distribution of temperature and salinity and in the transport of these properties by large-scale ocean circulation.

provide information needed for the calibration of satellite measurements.

deliver data for the initialisation and constraint of climate models.

Argo Australia is the second largest contributor to the global array (in terms of instrument numbers) after the US.

Argo Australia is operated by CSIRO Oceans and Atmosphere based in Hobart, Tasmania with financial and operational support from the Bureau of Meteorology, financial support from IMOS, CSIRO, the Antarctic Climate and Ecosystem Cooperative Research Centre and the Department of Climate Change and Energy Efficiency.

Instrumentation and Data

Argo floats have revolutionised our understanding of the broad scale structure of the oceans to 2000 m depth. Since the Argo program began 15 years ago, more high resolution hydrographic profiles have been provided by Argo floats then have been collected historically by traditional ship-based hydrography.

A typical Argo float mission is to profile from 2000 m depth to the sea surface every 10 days. On deployment, the float sinks to a park depth (e.g. 1000 m) and drifts with the ocean currents for 9 days. Then the float sinks deeper to its profile depth (usually 2000 m) before starting to ascend through the water column measuring temperature, salinity and pressure as it rises. When the float reaches the surface it transmits location and oceanographic measurements via satellite to land-based Argo data centres. After transmission the float sinks again and repeats the cycle.

Application of Data

The International State of the Climate in 2014 report confirmed that 2014 was Earth’s warmest year on record. IMOS data from Argo floats and ocean gliders contributed to NOAA's State of the Climate report published in July. In 2014, the most essential indicators of Earth’s changing climate continued to reflect trends of a warming planet, with several markers such as rising land and ocean temperature, sea levels and greenhouse gases ─ setting new records. These key findings and others can be found in the State of the Climate in 2014. To read more click here.

Heat content of the global ocean dominates the amount of stored heat in the climate system. A comprehensive study of the world’s oceans made possible by the global array of profiling Argo floats and published in Nature Climate Change has revealed the ongoing and steady rise of global ocean heat content. Temperature and salinity data from the 3881 Argo floats that make up the global array (of which IMOS through Argo Australia contributes 340 active floats) show that the warming signal extends to 2000 metres and deeper, and that it is occurring predominantly in the Southern Hemisphere ocean south of 20°S. The ability to consistently detect a global upper ocean heat gain over the short 2006–2013 period is historically unprecedented, and is due to the homogeneous global coverage, high data quality, and temporal resolution of seasonal and interannual fluctuations of the Argo observations. To read more click here.